The present invention relates to a method of changing the trigger threshold of a brake stand-by function of a vehicle brake.
The invention is based on a brake device, which is known by the name ‘brake assist system’. The origin of creating the brake assist system is the empiric observation that unskilled drivers do not depress the brake pedal with sufficient vigor in the event of a panic stop in order to achieve the maximum possible brake effect.
The brake assist system provides a remedy in this case upon detection of an emergency braking situation by building up higher brake pressure than would be corresponding to the position of the brake pedal. The graph of FIG. 1 shows this state of affairs.
FIG. 1 depicts three different curves, which display the variation of the brake pressure as a function of time t for three different types of drivers. Curve 1 describes the rise of the brake pressure in a panic stop for an average driver, curve 2 describes it for a skilled driver, and curve 3 for an average driver with a brake assist system.
FIG. 1 illustrates that an average driver manages to build up the maximum brake pressure more quickly with the aid of a brake assist system than without a brake assist system. This means that an average driver having a brake assist system—as can also be seen in FIG. 1—is even able to surpass the braking power of a skilled driver without a brake assist system. The faster pressure increase leads to a shorter stopping distance and, thus, enhances traffic safety.
In an improvement of the brake assist system, brake pressure is built up in the wheel brakes upon detection of an emergency braking situation already before the driver applies the brake pedal. The advantage of this system involves that the brake pads or brake shoes will move to bear against the brake discs or brake drums as a result.
Admittedly, no appreciable braking effect is accomplished by this action, but the response time of the brake is shortened because the clearance of the brake pads or brake shoes is overcome already prior to the application of the brake pedal. This function of the brake assist system is also referred to as brake stand-by function.
A major aspect of the proper functioning of the brake stand-by function is the reliable detection of an emergency braking situation.
In a method disclosed in DE 44 13 172 C2, an exceeding of a threshold value for the actuating speed of the brake pedal indicates that an emergency braking situation prevails. Active braking with maximum brake pressure is performed in response thereto. In this method, the return speed of the accelerator pedal is evaluated in order to adapt the threshold value for the actuating speed of the brake pedal.
In addition, it is known from DE 196 29 229 A1 to produce brake pressure in the wheel brakes in order to eliminate the clearance when the return speed of the accelerator pedal exceeds a predetermined threshold value.
In the prior art methods and devices, however, the difficulty may be encountered that it is impossible to make a reliable distinction between an emergency braking situation and a shifting operation as regards drivers with a sporty driving style who shift the gears quickly. The result may be that a sporty driving style and rapid upshifting maneuvers will trigger the brake stand-by function and insignificant deceleration occurs. However, this is in contradiction to the desire of the sporty driver to achieve maximum high acceleration.